Voltage clamp circuit connection

General discussion of using Roboclaw motor controllers
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Joined: Sat Jul 07, 2018 2:15 pm

Voltage clamp circuit connection

Postby nmendiv » Sat Jul 07, 2018 2:21 pm


I am designing the voltage clamp circuit for the MCP260 Motocontroller. I am not sure what option is correct about the connection of the gate of the transistor since in the text and the image there are different things and also in the topics published in this forum.

Where should be connected the pullup resistor R2? It has to be connected to +5VDC or to the negative battery lead (B-)?

Also, to confirm it, the transistor gate has to be connected to the negative lead (B-)?

Thank you very much

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Basicmicro Support
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Joined: Thu Feb 26, 2015 9:45 pm

Re: Voltage clamp circuit connection

Postby Basicmicro Support » Mon Jul 09, 2018 9:20 am

For MCP boards there are two options. Use a DOUT pin directly connected through a power resistor(2 to 10ohms 50watts or more) to B+. This will work for disipation upto 3.5 amps per DOUT pin.

Second option is using an external mosfet(like the one we recommend for Roboclaw voltage clamp circuits). There is a mistake in the diagram in the MCP user manual in regards to the pull-up/down resistor.

The wiring should be:

1. DOUT to mosfet Gate.
2. Pull-UP resistor(not pull-down) to 5v on the mosfet gate.

This is because the DOUT pins are open drain outputs only(eg they onlyy pull low so you need the pull-up to produce a high). The pullup resistor should be around 1k. The rest of the connection(drain and source pins on the mosfet) are shown correctly in the manual.

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